Two different sublines of the Dunning R3327 transplantable prostate adenocarcinoma are being investigated. These sublines, designated G and H at our institution, demonstrate in vivo and in vitro differences. The G subline is rapidly growing and poorly differentiated histologically, while the H subline grows very slowly and is a well-differentiated tumor. Lectin binding studies have demonstrated quantitative differences between the two tumors. Purified membrane preparations from the H tumor bind more concanavalin A (Con A) and Wheat Germ Agglutinins than do G tumor membrane preparations. These studies have been extended to monolayer cell cultures derived from G and H tumors. The H tumor cells bound more con A than did the G cells, while further analysis of these kinds of experiments suggests a heterogeneity of binding sites of both G and H cells in culture. Tumors and cells in culture analyzed by flow cytometry have demonstrated the tumors to consist of at least two populations of cells; one diploid and one aneuploid. Cell separation techniques and cloning experiments are underway to identify the tumor cell. Antibody has been produced in goats to purified membranes of the G and H tumors and in rabbits to whole tumor cells. Fractionation of the immunoglobulins and affinity chromatography have resulted in the isolation of an antigen. The tumor specificity of this antigen is under investigation.